Communication devices such as wireless devices are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a communications network or wireless communication system, sometimes also referred to as a radio system or networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The communications network may covers a geographical area which may be divided into cell areas, wherein each cell area being served by an Access Node (AN) such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Communications such as transmissions in radio communication systems are often organized in terms of frames, or sometimes subframes, e.g. in LTE, where each frame is a group of communication resources, e.g., radio time and frequency resources, that may comprise both, a control field and a payload data field, or multiple fields of the respective types. A field is understood herein to refer to a set of time and frequency resources, also referred to herein as time-frequency resources. Examples of time-frequency resources are symbols, resource elements, OFDM symbols, Filter-Bank Multi-Carrier (FBMC) symbols, symbols of some of the type of multi-carrier modulation scheme, a set of any of the mentioned types of symbols, etc. . . . . The time-frequency resources corresponding to a field may be contiguous in the time and frequency dimensions. The control field may, e.g., comprise information about how the data part of the frame is encoded and modulated. The control field may also be used for receiving feedback information in the reverse link direction, i.e., from the receiver of the data, e.g., for receiving ACKnowledgement/Negative ACKnowledgement (ACK/NACK) or channel state information reports.
Half-Duplex
In many radio communication systems, communication nodes are only capable of half-duplex communication, i.e., a network node, e.g., an AN or a UE, may not both transmit and receive at the same time, at least not on the same frequency band. The main reason for such a limitation is that a network node that is transmitting may saturate its own analog receiving circuitry due to overhearing between transmit and receive antennas.
An implication of this is that data may only be communicated, e.g., transmitted, in one link direction at a time. However, even for one-directional data communication, there is, as explained above, normally a need for regular communications of control information in both link directions, implying that in half-duplex communications, it may be useful to have two fields for control information in every frame, one for one link direction, and one for the reverse direction. Two fields may be useful also in full-duplex systems, but for other reasons. The two directions of a link will henceforth be referred to as Transmit/Receive (tx/rx) directions, or sometimes the two duplex directions. In other words, any given communication node may use one of the fields for transmission (tx) and the other field for reception (rx). The link direction may also be referred to herein as a direction of communication.
Communication as used herein, refers to one of transmission or reception, which may be also referred to collectively as “transmission”, such as a transmission of data or a transmission of control information. Control information refers herein to, e.g., channel state information, reception acknowledgement reports such as ACK/NACK reports, other types of feedback, Medium Access Control (MAC) messages, information about coding and modulation schemes used in associated data transmissions, other types of system link configuration messages, etc. . . . . Data information refers herein to, e.g., payload data, which may in turn contain data information as well as control information for higher layers in the protocol stack.
Frame Structure
A possible frame structure and link-direction assignments is illustrated as a schematic diagram in FIG. 1, cf. also “Time-division duplexing”, WO 2014/121833 A1 (PCT/EP2013/052376). Any two communication nodes communicating may in principle arbitrarily select which of the two control fields may be used for tx and which for rx, see left and right panels of FIG. 1. However, such arbitrariness may require complicated negotiation procedures and hence it is often more practical to have a general rule for the system, e.g., that one of the fields is always used for DL communication, i.e., tx by ANs, whereas the other field is always used for UL communication recepion, i.e., tx by UEs, see the illustration in FIG. 2 for a schematic diagram of another possible frame structure and respective link-direction assignments. Note also that frames on different links in the system may preferably be time-aligned, partly because this enables communication nodes to more freely and efficiently change communication partner, that is node, from one frame to another, without waiting for the other communication link to finish its frame.
Fields are in most transmission systems further divided into smaller units, e.g., in Orthogonal Frequency-Division Multiplexing (OFDM) systems, the fields may be further divided into one or more OFDM symbols. Similar holds for many other types of systems than OFDM, e.g., for many systems based on multi-carrier or pre-coded multi-carrier such as FBMC, Discrete Fourier Transform (DFT)-spread OFDM, etc. As a general term, such smaller units are referred to herein as symbols. Some fields may consist of only a single symbol.
Other Signals and Fields in and Between Frames
Switching of tx/rx direction may take some time, and therefore, may require an extra guard period between adjacent symbols that belong to fields with different duplex direction. Moreover, it should be noted that within the three fields, there may typically also be other signals interspersed, e.g., reference signals, or pilot signals, to allow the receiver to perform channel estimation. For simplicity, guard periods or other signals are not shown in these figures.
Self-Backhauling
In the case of radio communication systems with very dense deployment of ANs, as envisioned in particular for systems operating at millimeter-Wave (mmW) frequencies, it may be difficult and costly to provide a wired backhaul connection, that is, a connection with the core network or Internet, to all ANs in the system. One option is to use wireless backhaul, i.e., have one AN with wired connection, henceforth referred to herein as Aggregation Node, or AgN, that forwards data to the other ANs wirelessly over a route, see illustration of a network using wireless self-backhauling in FIG. 3. In the more general case, the routes may form a more complicated pattern, e.g. a route tree. A particularly attractive solution is to use wireless self-backhauling, i.e., use the same frequency spectrum for access links and backhaul links, which avoids the need for multiple radio units in each communication node. Note that in such a network, not only user data may have to be forwarded over the backhaul links, but also control signaling for, e.g., radio resource coordination between ANs, e.g., allocation of time-frequency radio resources and scheduling on access links, or for setting up routes, may have to be performed wirelessly.
Communication networks such as those with very dense deployments of communication nodes, may require exchange of control information among a number of communication nodes, or even all of them, within a certain time period, e.g., a frame. However, current frame structures do not provide for such communication.
Also, communication networks such as those with very dense deployments of communication nodes or such as those with a combination of self-backhauling and half duplex, may require performance of measurement procedures among a number of communication nodes, or even all of them, within a certain time period, e.g., a frame. With current frame structures, a communication node is allowed to perform particular types of measurements. Hence, control of interference or other types of signals in a communications network, leads to underperformance of communications in the network.